Location of insulation defects in power transformer based on energy attenuation analysis

Power and distribution transformers form important components in the electricity grid. Failure of such important components can give rise to high costs (such as costs for repair and cost for non-delivery). Therefore means to determine the risk of failure of transformers are of importance. For on-line partial discharge detection in transformers, the UHF technique has been introduced several years ago. In this paper a technique to locate the discharging insulation defect is introduced, based on the energy content in the frequency spectra, detected on all couplers. It is known that the energy, radiated by the PD source, is attenuated by the distance and due to propagation in oil. Therefore, a two-steps procedure is necessary and is described in this paper: a correction matrix is defined based on a sensitivity check which is then used to correct actual PD measurement results. Results are shown from calibration measurements on and PD testing of a 150 MVA power transformer.